It is known in the prior art to place the wire part, the press section, and/or the dryer section of a paper machine inside a hood. The aim of the placement of the wire part in a hood has been in particular to prevent spreading of moisture drops into the machine shall. In the area of the press section, the hood is provided in view of energy economy enabled thereby, and thus there has been an attempt to obtain such energy efficiency as the pressing of the paper web is accomplished more efficiently because the web and the felts that are used are warmer as a result of the placement of the hood. It is a further object of the hood to operate as a noise insulation mechanism and to separate the wire part and the press section from the rest of the machine hall, in which case the hood prevents spreading of moisture into the machine hall. In the dryer section, by means of the placement of a hood in connection therewith, attempts are made in particular to reduce the consumption of energy and to prevent spreading of heat, moisture and noise into the machine hall.
With respect to prior art related to the dryer section and the placement of a hood in connection therewith, reference is made, for example, to the publication Wochenblatt fur Papierfabrikation 23/241992, by F. Sodec, entitled "Neues Haubenkonzept fur energiesparende Papiertrocknung". In this publication, an exemplifying embodiment is described of a concept in which, in the dryer section, a hood and an air-conditioning arrangement are employed.
With respect to additional prior art related to the dryer section, reference is made to Finnish Patent 63,980 (which corresponds to U.S. Pat. No. 4,536,970, which is incorporated by reference herein), in which a method is suggested and disclosed for enhancing the air-conditioning in dryer sections provided with a closed hood in paper machines. In this patent, particular emphasis is placed on arranging the air-conditioning, or other air-control system, of the hood so that problems arising from condensation can be prevented.
With respect to hood arrangements related to the press section of a paper machine, reference is made to Finnish Patent 83,551, in which a press section of a paper machine is described in particular a press section in which suction rolls are used. According to FI 83,551, the press section is covered with a hood, whose construction is such that it both raises the temperature of operation of the press section and reduces the noise level in the environment outside the press section to a substantial extent. In the arrangement in accordance with FI 83,551, the hood comprises of displaceable wall and ceiling elements positioned at the tending side and displaceable or fixed wall elements positioned at the driving side. These elements of the hood are made of a sound-insulating material, which is at least partially transparent at the tending side. The description of the inventions in FI 83,551 constitutes the prior art most closely related to the present invention.